developerlife – Tutorials » Creating a BlackBerry custom field

Creating a BlackBerry custom field

Posted October 10th, 2009 by Nazmul

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Introduction

This tutorial will show you how to create a very simple custom field (component) using the RIM API. If you’re familiar with Swing, then this code will not be a surprise to you. There are some similarities between AWT/Swing and RIM UI API.

Example

I’m going to create a custom label field that is different from the LabelField in that you can set a foreground color on it. Here’s the code to do this.

public class MyLabelField extends LabelField {

  private String text;
  private int fgColor;

  public MyLabelField(String text, int fgColor){
    this.text = text;
    this.fgColor = fgColor;
  }

  // @Override
  protected void layout(int w, int h){
    setExtent(w, Font.getDefault().getHeight());
  }

  // @Override
  protected void paint(Graphics g){
    g.setColor(fgColor);
    g.drawText(text, 0, 0);
  }

}

This is what’s going on in the code:

The constructor of MyLabelField simply accepts a label text and foreground color. Note that this class extends LabelField.
The paint() method has been overridden (just like in AWT or Swing) to provide custom painting code for this class. Here I just set the foreground color and write the string out with it.
The layout() method has been overridden. You have to do something similar in Swing/AWT but the syntax here is totally different. The layout method is called by a layout manager to size and position this field on the screen. So all this method does is it returns its preferred dimensions, by calling setExtent(). The layout() method is called first, before getExtent(), by a layout manager, so it’s important that you set the extent in this method.

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Further reading in related categories

BlackBerry

Creating a BlackBerry HTTP Connection: This tutorial will show you the various ways to create an HTTP networking connection from your BlackBerry device to an HTTP server (web service, servlet, etc). The complicated part about doing this on a BlackBerry is deciding which transport you would like to use, and which transport you can use.
BlackBerry field borders and backgrounds: This tutorial will show you how to create field (component) backgrounds and borders (decoration). Each field can have a border and a background property. You can use the border to space out fields in your UI, and you can use them to add whitespace. The background allows you to set the background color property of your field and make it fit the look for your app.
Using the BlackBerry gauge field to display progress: This tutorial will show you how the use the gauge field to show progress in your apps. This is useful when your app is performing long running tasks that need to report feedback to the user. The gauge field is a horizontal component that can be used to display status or progress. It displays a percentage from 0 to 100 and you can set a label before it to display any progress/status messages. You can even overlay the label inside of the gauge field, so that it won't be displayed before it, but inside of it (on top of the progress bar that’s drawn).
Asking for BlackBerry application permissions upfront: This tutorial will show you how to ask a user (of your BlackBerry app) for permissions that are required in order for your app to function properly. There are many APIs in the RIM API that will cause a prompt to be displayed in the BlackBerry UI that will require a user to provide explicit permission to access certain API functionality or access to certain hardware features or data on the device. Instead of interrupting the UI, it’s possible to ask the user for all of these permissions at the very beginning. By the way, if the user does not grant permissions when this popup appears, then an exception will be thrown which you have to deal with.
Working with BlackBerry screens: In this tutorial, I will show you how to quickly manage screens using the RIM UI API. The BlackBerry OS maintains a stack of screens, and your app can be pushed and popped from this stack. These are normal screen display operations. You can even hide your screen from the display, and it will show the BlackBerry home screen. You can close the screen as well.
Working with BlackBerry Layout Managers: This tutorial will simply walk you through the various layout managers available to you using RIM’s UI API (not MIDP). RIM’s layout managers are akin to Swing layout managers, and allow you to arrange lots of fields (aka components in Swing), on the screen. You can create your own layout managers, just like in Swing, but this tutorial will show you how to use the built in ones. If none of the layout managers shown here work for you, then you can composite layout managers to get the desired look for your app, before creating your own.
Creating your first GUI BlackBerry App: This tutorial will simply walk you through creating your first GUI app using RIM’s UI API (not MIDP). Only a skeleton will be created, that you can later expand on to create your own projects.
Using JSON for mobile object exchange: I've been working with various object encoding schemes to get information transferred over the network between services and mobile apps running on Android and BlackBerry. On Android, I figured I would try using Java object serialization, and that works some of the time, and not for anything complex. I wish the object serialization and deserialization mechanism in GWT would be ported over to all these mobile environments, but I digress. This tutorial outlines the use of JSON for this purpose.
Getting code signing keys from RIM, then using them: If you use certain BlackBerry APIs, you have to get code signing keys and sign your .COD file with them, before you will be able to install and run these applications on a BlackBerry device. This tutorial will walk you through the process of getting the keys, and installing them to your JDE, and then deploying your application to a real device OTA (over the air).
BlackBerry Development Tools - JDE (and IDEA): There are different tools that you can use for BlackBerry development - Eclipse Plugin and JDE. In this tutorial I will show you how to use the JDE in conjunction with IDEA as the primary IDE for BlackBerry development. Directions are provided on how to install and configure the JDE, then get started with a Hello World project, then deploy the project to the simulator and run it. The JDE is an IDE that BlackBerry created, and it's really really old. Modern IDEs like IDEA, Eclipse, and NetBeans really put it shame. It's good to see that BlackBerry is working on an Eclipse based IDE, and hopefully the JDE will be retired soon. I couldn't stand to use the JDE by itself, which is why I do all my editing, compiling, refactoring in IDEA, and just use JDE to build my COD file and run it in the simulator, and occasionally use the debugger in the JDE. It's really old looking and clunky, and just a pain to work with, when compared to IDEA. You can use Eclipse or NetBeans instead of IDEA if that's your preference.
BlackBerry Development Tools - Eclipse Plugin (in beta): There are different tools that you can use for BB development - Eclipse Plugin and JDE. In this tutorial I will show you how to use the Eclipse Plugin as your IDE for BlackBerry development. Directions are provided on how to install and configure the Eclipse Plugin, then get started with a Hello World project, then deploy the project to the simulator and run it.
BlackBerry SDK and tools - Getting Started: This tutorial has helpful pointers for developers who are just getting started with Blackberry development. This includes information on tools, IDEs, tutorials, videos, etc.

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Related Categories: BlackBerry | Related Tags: BlackBerry, ui stuff

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